Impellers for fans of this type must meet several requirements, including: low noise; good noise spectrum distribution; high efficiency; dimensional compactness; good pressure head and capacity.
Document EP-0 816 687 discloses a centrifugal fan having an impeller with inclined blades.
The blades are arranged on an annular surface around the impeller axis. Each blade has a tapering section and is curved outward, that is to say, has edge portions that are curved outward.
This constructional design, although it effectively reduces noise, is difficult to make by plastic injection moulding. Thus, document EP-0 816 687 also proposes a specific method for manufacturing the impeller and moulds especially designed for this purpose.
The present invention has for an aim to provide an improved, low-noise centrifugal fan impeller with inclined blades which offers top performance in terms of pressure head and capacity and which, at the same time, is easy to construct.